1. Field of the Invention
The present invention relates to a gas turbine exhaust passage applied to simple cycle gas turbines and combined cycle gas turbines having a bypass chimney or the like and to a damper system for same.
2. Description of the Related Art
FIG. 8 shows a conventional simple cycle gas turbine exhaust passage, and FIG. 9 shows a conventional combined cycle gas turbine exhaust passage. In FIG. 8, the exhaust passage is connected to a gas turbine body 1 through an exhaust diffuser 2 and is composed of an exhaust duct 3 provided with an internal exhaust silencer 4, and an exhaust chimney 5 connected to the exhaust duct 3. On the other hand, in FIG. 9, the exhaust passage is connected to the gas turbine body 1 through the exhaust diffuser 2 and is composed of an exhaust duct 3 provided with an internal exhaust silencer 4, and a bypass chimney 6 connected to the exhaust duct 3.
The general cross-sectional structures of the walls of the above-described conventional gas turbine exhaust passages are shown on an enlarged scale in FIGS. 8 and 9. In general, two types of cross-sectional structures are used. The enlarged cross-sectional structures shown in portion D in FIG. 8 and portion F in FIG. 9 are those used in the exhaust ducts 3 of the respective exhaust passages. In these cross-sectional structures, a heat insulating material 32 is sandwiched between an inner plate 31 and an outer plate 33. Also, the enlarged cross-sectional structures shown in portion E in FIG. 8 and portion G in FIG. 9 are those used in the exhaust passage chimney 5 or the bypass chimney 6 of the respective exhaust passages. In these cross-sectional structures, a refractory member 52 such as refractory bricks is lined on the inside of the outer plate 53. There is no gas permeability or acoustic transmissivity with either of these structures.
Also, as shown in FIG. 9, in the case of a combined cycle gas turbine exhaust passage, a boiler inlet duct 7 connected to the chimney 10 through an exhaust gas boiler 8 is connected to the exhaust duct 3. A bypass damper 9 is provided at a joint portion between the boiler inlet duct 7 and the exhaust duct 3. Also, as with the cross-sectional structure of each of the above-described walls, the bypass damper 9 has a structure with which there is no air permeability or sound transmissivity. The gas flow and the acoustic characteristics in the exhaust passage during the bypass operation are substantially the same as those of the exhaust passage shown in FIG. 8.
In the gas turbine exhaust passage having the conventional cross-sectional wall structure, pressure pulsation and high speed exhaust gas flow turbulence generated in a combustor of the gas turbine are amplified at a resonant frequency of the exhaust passage and an ultra low frequency noise in the range of 10 to 30 Hz is emitted from the opening of the chimney. As a result, ultra low frequency noise trouble occurs. Since portions other than the chimney opening are acoustically sealed due to the cross-sectional structure of the walls of the exhaust passage and the bypass damper, the damping of the sound field is small and the resonance magnification is high. Hence, such trouble occurs.
Accordingly, an object of the present invention is to provide an exhaust passage which can maintain a good environment without causing the ultra low frequency noise trouble.
According to the present invention, a gas turbine exhaust passage having a wall for defining an exhaust passage for discharging exhaust gas of a gas turbine is characterized in that at least a portion of the wall is formed of acoustically transmissive material for allowing sufficient low frequency noise of several tens of Hz or less to pass therethrough.
With this arrangement, since at least a portion of the wall is formed of an acoustically transmissive material, the damping effect of an acoustic field within the exhaust passage is enhanced to make it possible to reduce resonance magnification. Hence, it is possible to suppress radiation of the strong ultra low frequency noise generated in the gas turbine to the outside.
Also, the gas turbine exhaust passage according to the present invention is characterized in that the acoustically transmissive material is made of at least one material selected from the group essentially consisting of a porous material, porous heat insulating material, mesh having a large flow resistance, and cloth or film material.
With this arrangement, since porous material, porous heat insulating material, mesh having a large flow resistance, and cloth or film material may transmit sound sufficiently, it is possible to further suppress radiation of the strong ultra low frequency noise generated in the gas turbine to the outside.
The gas turbine exhaust passage according to the present invention is further characterized in that the acoustically transmissive material is supported by a porous plate or frame.
With this arrangement, since the acoustically transmissive material is supported by the porous plate or frame, the acoustically transmissive material may be used even if the transmissive material can not maintain its shape.
Also, a damper system for a gas turbine exhaust passage, comprising a gas turbine exhaust passage for discharging the exhaust gas of a gas turbine, an exhaust gas boiler branched from the gas turbine exhaust passage, and a damper provided at a branch portion between the exhaust gas boiler and the gas turbine exhaust passage, is characterized in that the damper is made of an acoustically transmissive material that can sufficiently transmit a low frequency noise of several tens of Hz or less.
With this arrangement, the damper provided at the branch portion between the gas turbine exhaust passage and the exhaust gas boiler is made of the acoustically transmissive material. Accordingly, the sound waves generated in the gas turbine are transmitted to the exhaust gas boiler through the damper. The sound waves transmitted to the exhaust gas boiler are absorbed by the exhaust gas boiler because the exhaust gas boiler has a large volume. Hence, it is thus possible to suppress radiation of the strong ultra low frequency noise from the gas turbine exhaust passage to the outside.
Also, according to the present invention, a gas turbine exhaust passage having a wall for defining an exhaust passage for discharging exhaust gas of a gas turbine, comprising an exhaust duct connected to a gas turbine body through an exhaust diffuser and provided with an internal exhaust silencer, and an exhaust chimney connected to the exhaust duct, is characterized in that at least a portion of the wall is formed of acoustically transmissive material for allowing low frequency noise of several tens of Hz or less to pass therethrough sufficiently.
Also, according to the present invention, a damper system for a gas turbine exhaust passage, comprising an exhaust duct connected to a gas turbine body through an exhaust diffuser and provided with an internal exhaust silencer, a bypass chimney connected to the exhaust duct, an exhaust gas boiler branched at a branch portion from the exhaust duct, and a damper provided between the exhaust gas boiler and the exhaust duct, is characterized in that the damper is formed of an acoustically transmissive material for allowing low frequency noise of several tens of Hz or less to pass therethrough sufficiently.
In any of the above cases, it is possible to suppress the radiation of the strong ultra low frequency noise to the outside.
Also, according to the present invention, a gas turbine exhaust passage having a wall for defining the exhaust passage for discharging exhaust gas of a gas turbine, comprising an exhaust duct provided with an internal exhaust silencer and an exhaust chimney connected to the exhaust duct, is characterized in that the wall of the exhaust duct has a structure having no gas permeability and acoustic transmissivity, at least a portion of the wall of the exhaust chimney is formed of an acoustically transmissive material for allowing sufficient low frequency noise of several tens of Hz or less to pass therethrough, and a rack is provided as surrounding and supporting the exhaust chimney.
In the above arrangement, since the wall of the exhaust chimney has a structure having acoustic transmissivity, an emission of the ultra low frequency noise can be restrained and transmission of noise from the wall of the exhaust duct can be prevented. Therefore, the risk of an accident caused by spouting an exhaust gas can be eliminated, thereby being capable of lightening and simplifying the wall structure of the exhaust chimney.
Further, the gas turbine exhaust passage, according to the present invention, is characterized in that at least a portion of the side and top of the frame formed the rack is provided with a soundproof panel.
In the above arrangement, noise emitted from the exhaust passage is absorbed and reduced by the soundproof panel.